[Gb-ccb] CCB interface questions

[Martin Shepherd]

On Fri, 12 Mar 2004, Randy McCullough wrote:
>...
> Then, as I understand it, the "PHASE STATES" are related to the "BINS" as
> follows...
>
> The "PHASE STATES" run chronologically as...
>
>     "PHASE STATE"    SWITCH A       SWITCH B
>
>           00           0           0
>           01           0           1
>           11           1           1
>           10           1           0
>           00           0           0
>           01           0           1
>           11           1           1
>           10           1           0
>           etc...       ec...       etc...
>
>      (Which uses "quadrature" to minimize the switching rate of each
> switch.)

When both switches are enabled, this is indeed the cycle that will be
used when the 'closed_switches' configuration register specifies that
both switches must start open at the beginning of each cycle. The
other possible dual-switch cycles, will be the same, but start at
different points in this cycle, to accomodate the closed_switches
parameter. This unfortunately isn't quite the same as shown in figure
3.1 of my network interface specification, where the final pair of
possible cycles follow the above cycle backwards. Clearly
phase-shifting the basic cycle that you show above makes more sense
than what I showed in that document, since then I can use a single
state machine within the FPGA, started at the state dictated by the
'closed_switches' parameter. It also makes it easier to remember what
happens for a given value of closed_switches, without having to look
at my document.

Clearly my network interfaces document needs revising, as does my
device driver document, but I'm too busy with the hardware side of
things to do this right now.

> And writing to the corresponding "BINS" goes as follows...
>
>    "PHASE STATE"    SWITCH A      SWITCH B     "BIN"
>
>          00             0             0          0
>          01             0             1          1
>          11             1             1          3
>          10             1             0          2
>          00             0             0          0
>          01             0             1          1
>          11             1             1          3
>          10             1             0          2
>etc...
>
> Is this correct???

Yes, that looks correct.

Martin